Canis ISSN: 2398-2942

Hyperthermia

Synonym(s): afebrile hyperthermia, inadequate heat dissipation (heat stroke), exercise induced hyperthermia, pathological hyperthermia, malignant hyperthermia

Contributor(s): Kyle Braund, Poppy Gant, Stefano Cortellini

Introduction

  • Hyperthermia: an elevation in core body temperature above accepted normal ranges secondary to an imbalance between heat production and heat loss.
  • Distinguish from true fever (or pyrexia) - the body’s normal response to endogenous pyrogens (produced during  infection, inflammation or injury). It is associated with an increase in the ‘set point’ in the thermoregulatory center in the hypothalamus. 
  • Pathophysiology: heat production exceeds heat loss.
  • Signs: variable based on severity and duration but can include altered mentation, hyperdynamic state and tachypnea with progression to collapse, hypotension and evidence of multi-organ involvement. 
  • Diagnosis: based on history, physical examination (NB temperature may be normal depending on owner care). Baseline blood tests may determine development of secondary organ injury or underlying disease process.
  • Treatment: focuses on active cooling.
  • Prevention: minimize environmental risk factors , exposure to triggers, control underlying disease.
  • Prognosis: dependent on severity and duration and underlying disease.

Pathogenesis

Predisposing factors

Heat stroke

  • Patient related:
    • Large dog breeds.
    • Obesity.
    • Brachycephalic breeds.
    • Males.
    • Dark coat colors.
    • Very young or old animals may be less able to increase heat dissipation.
  • Environment related:
    • Hot environment.
    • High humidity.
    • Inadequate ventilation.
    • Close confinement.

Other

  • Small breed dogs more likely to reach toxic dose of drug exposure.
  • Dogs that scavenge are more likely to be exposed to intoxications.
  • Certain breeds of dog are considered predisposed to malignant hyperthermia Malignant hyperthermia:
    • Greyhounds, Labrador Retrievers, Saint Bernards, Pointers, Dobermans, Border Collies, English Springer Spaniels.

Pathophysiology

  • Information from peripheral and central thermoreceptors is normally conveyed to the hypothalamus in order to tightly regulate body temperature.
  • If required, the hypothalamus can stimulate heat loss mechanisms, eg panting, vasodilation, behavioral and postural changes to aid heat dissipation.
  • Hyperthermia results when physiological, pathological or pharmacological changes cause heat production to exceed heat loss.
  • Temperatures above 41.6°C (106.88°F) can start to cause cellular damage secondary to relative hypoxemia Hypoxemia.
  • Exertional heat stroke Heat stroke and malignant hyperthermia Malignant hyperthermia can also cause rhabdomyolysis Exertional rhabdomyolysis with myoglobinemia.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • (See references for Heat stroke Heat stroke.)
  • Stern A (2019) Canine enviromental hyperthermia: a case series. J Vet Med Sci 81(2), 190-192 PubMed.
  • Carter A J, Hall E J (2018) Investigating factors affecting the body temperature of dogs competing in cross country (canicross) races in the UK. J Therm Biol 72, 33-38 PubMed.
  • Adami C et al (2012) Unusual perianesthetic malignant hyperthermia in a dog. JAVMA 204(4), 450-453 PubMed.
  • Thomas E K, Drobatz K J, Mandell D C (2014) Presumptive cocaine toxicosis in 19 dogs: 2004-2012. JVECC 24(2), 201-207 PubMed.
  • Fitzgerald K T, Bronstein A C (2013) Adderall® (amphetamine-dextroamphetamine) toxicity. Top Companion Anim Med 28(1), 2-7 PubMed.

Other sources of information

  • Miller J (2015) Hyperthermia and Fever. In: Small Animal Critical Care Medicine. Silverstein D & Hopper K (eds). Chapter 10.
  • Drobatz  K (2015) Heat Stroke. In: Small Animal Critical Care Medicine. Silverstein D & Hopper K. Chapter 167.
  • Gwaltney-Brant S M (2013) Miscellaneous indoor toxicants. In: Petersen M E, Talcott P A, (eds) Small Animal Toxicology. St. Louis, MO: Saunders; 3rd edn,  pp 291-308. 


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